1. Field of the Invention
The present invention relates to design techniques of circuit for increasing Q ratio by adding a negative resistor to a tuning circuit using an inductor and a capacitor.
2. Description of the Related Art
In order to improve a frequency selectivity of receiver, it may substantially have a large Q ratio of a tuning circuit of the receiver. However, it is adopted that a high frequency amplifier and a tuning circuit are added to the receiver, for it is difficult to improve the receiver so as to realize a marked difference improvement more than present receiver by means of material design or physical structure of inductor mainly. However, such method has a difficult troublesome that pertain two or more tuning frequency must be accurate interlocked.
As an another method, there is a method to increase Q value of the tuning circuit directly using a negative resistance circuit. The method had been many used as a regenerative detection system until a heterodyne system is developed. However, it is necessary to set up a positive feedback circuit manually in every time a tuning frequency is changed.
The object of the present invention is to realize a Q value of a tuning circuit capable of setting up a fixed value automatically when the Q value of the tuning circuit is increased using a negative resistance circuit without above-mentioned drawbacks in that the turning circuit is set up manually.
In order to achieve the above object, one aspect of the tuning circuit according to the present invention, a subject matter of the invention has an inductance and a capacitor and a negative resistance circuit connected to the resonance circuit in series, comprising:
a setting means for calculating a serial resistance value having said resonance circuit and setting up a negative resistance value of said negative resistance circuit using said serial resistance value and a resistance value for obtaining a necessity Q value to an optimum resistance value.
In the present invention, the setting means may be constituted to make an effective serial resistance of said tuning circuit be in weak oscillation state by controlling a negative resistance of said negative resistance circuit and to do operations;
for detecting an oscillation amplitude value at changing a negative resistance value;
for calculating said serial resistance value;
for subtracting from resistance value for obtaining said necessity Q value to the serial resistance value; and
for setting up said optimal resistance value.
In the present invention, it is preferred that the tuning circuit may comprise means for separating said setting means from an input/output of said tuning circuit.